This spell had two very different effects depending on where it was cast. If cast upon land the spell opened a gate to the Para-Elemental Plane of Magma, immediately filling the area with molten lava. Any creature in the area unable to fly or escape by other means began to sink into the lava, suffering excruciating damage from contact with the molten rock. The area of effect for this spell depended on the skill of the caster, but typically measured hundreds of cubic feet. The lava would remain until successfully dispelled or until it cooled to solid rock after several days.
Eruption was fully capable of destroying buildings and other structures.
If eruption was cast in a body of water whose volume was greater than the effective area of the spell, then the spell failed. If the effective spell area was greater then it created a giant cloud of scalding steam the same size as the body of water. The intense heat from the steam harmed all creatures caught within before dissipating after 5-10 minutes. Spells such gust of wind could also dissipate the steam.